The purpose of this proposal is to characterize the apoprotein(s) of human pulmonary surfactant using state-of-the-art electrophoretic techniques in conjunction with immunochemical methods. This is the first step of a detailed study of the intracellular and extracellular metabolism of the apoproteins. Specifically, the various forms of surfactant apoprotein will be identified in surfactant obtained from various human sources, including the human lung cell line, A549, which synthesizes and secretes at least two forms of surfactant apoprotein. Using these cells, the synthesis, intracellular processing and extracellular processing will be examined by electrophoresis, peptide mapping, isotopic labelling studies and immunochemical methods in order to determine the relationship between these proteins. Messenger RNA from these cells will then be translated in a cell-free system in order to identify the primary translation product(s) and determine whether the various forms of surfactant apoproteins are derived from a single precursor molecule or are separate gene products. From these studies, information will be gained about the properties of the proteins that will be useful for their purification as well. This will permit the testing of homogeneous preparations of various surfactant apoprotein forms with natural and artificial surfactant preparations. Well-characterized forms of surfactant apoproteins may provide more specific endpoints for the study of hormonal regulation of fetal lung muturation than phospholipid profile and morphology have offered to date. Studies of the regulation of these proteins may then permit more effective clinical detection and intervention in the prevention and treatment of neonatal respiratory distress syndrome.